Coupling device



Oct. 14, 1930. N. E. LINDENBLAD COUPLING DEVICE Filed March 23, 1928 a m m 5 6 lg I? I: I w 2 so 47 J INVENTOR NIL 1? Patented Oct. 14, 1930 UNITED STATES PATENT OFFICE NILS E. LINDENBLAD, 0F ROCKY POINT, NEW YORK, ASSIGNOR TO RADIO CORPORA- TION OF AMERICA. A CORPORATION OF DELAWARE COUPLING DEVICE Application filed March 23, 1928. Serial No. 264.132.

This invention relates to coupling devices, and more particularly to a method and means for so coupling circuits having different impedances that their impedances are matched.

It is customary to match the impedance of transmission lines in order to make them refiectionless, and inasmuch as the circuit or other transmission line branch to which the line is to be coupled may not have the proper impedance to match that of the line it is often necessary to use impedance matching devices. Such device's have ranged all the Way from simple transformers for low frequency energy to complex combinations of inductors and condensers for energy of high frequency. These units are difiicult to design for outdoor use, and it is therefore necessary to enclose them in weather proof compartments. This not only adds to the apparatus itself, but requires additional equipment for supporting the compartment with its enclosed circuits.

It is a primary object of my invention to provide an impedance matching device requiring no inductor and condenser units. no enclosure. and no external support. For this purpose I couple the lines to be matched symmetrically to a linear oscillator. and so space the points of coupling of each of the lines to the oscillator that the desired impedance between the points of coupling is obtained.

This arrangement is exceedinglv simple. comprising merely a piece of conductor arm ranged transversely of the line. but it. tends to radiate energy. and to overcome this ditli cultv is a further object of mv invention. which I fulfill by bending the oscillator in the direction of the line. or in the case of an ungrounded oscillator. in bifilar form. which effectively prevents radiation.

It is customary to provide for melting the sleet on outdoor antennae and their feed lines by sending a heavy direct current or low frequencv current through the various portions of the line and antennae. The couplin oscillator so far described short Circuits the sleet melting current. to overcome which difficulty is a further obiect of my invention. ac-

complished simply by inserting a blocking condenser at the potential node or center of the oscillator. This condenser, while of negligible reactance for the radio frequency cur rent, is effective to separate the two halves of the oscillator with respect to the sleet melting current.

The impedance matching device may be left exposed without serious effect, but to avoid even the slight detuning which might be caused by considerable formation of sleet I provide the oscillator itself forsleet melting. To this end I utilize two linear oscillators connected at their ends or current nodal points, and each having a blocking condenser at the center or the potential nodal point, so that the oscillators are connected in parallel with respect to the high frequency energy, and in series with respect to the sleet melting current. One of the transmission lines is synnnetically coupled directly to one of the oscillators at points so spaced that the impedance therebetween matches the impedance of the line coupled thereto. and the other line is directly symmetrically coupled to the other oscillator at points so spaced that its impedance also is matched. In effect. each half of the oscillator is made like a hairpin. so that the. sleet melting current flows up and back in each half of the oscillator.

A further object of my invention is to make the device self-supporting under tension when connected directlv in the line. It has already been mentioned that to prevent radiation the oscillator is bent in bifilar form. lVith two oscillators such as has been described to provide for sleet melting the oscillators may be bent into bifilar form in opposite directions. and the U shaped portions connected end to end. In final form the impedance matching device consists simply of an insulated section of transmission line directly tensioned between the lines which are to be coupled together through four tension insulators. with means including blocking condensers connecting the two lines of the insulated section of line together at their ends. the length of the insulated or closed trap circuit being suitable to resonate the energy being carried on the lines. and

in addition four short conductors or jumpcrs conncctlng each of the lines outside of ing one, or any other reason.

the tension insulators to the line inside the insulators at such oints that the impedance therebetween matc es the impedance of the Figure 5 is like Figure 4 except that the oscillators are bent in opposite directions;

Figure 6 shows my invention in preferred form, and

Figure 7 is a modification applied to a single wire transmission line.

Referring to Figure 1 there is a line 2- -4, which is to be coupled to another line 6-8, of different natural impedance. This difference may be caused by a difference in dimension, or by reason of several lines join- In accordance with my invention a simple linear oscillator, such as the wire 10, approximately a half wave long or tuned to the frequency of the energy being carried on the lines, is positioned transversely of the lines, and the latterare each coupled to the oscillator at points symmetrically located with respect to its mid-point, and so spaced that the impedance between the points of coupling of the lines 2-4 matches the impedance of the line 24, while the impedance between the points of coupling of the line 6-8 matches the impedance of the line 68. The

potential and current distribution on the oscillator 10 are indicated by the curves 12 and 14 respectively.

To PIOVldB for sleet melting it is customary to feed a direct or low frequency current through the lines 2-6 and 8 4 in series, and to prevent short circuit by the linear oscillator a blocking condenser may be provided at the potential node or midpoint of the oscillator, as is indicated by the blocking condenser at the mid-point of the oscillator 10 in Figure 2. The oscillator may itself be provided for sleet melting by slight additional complication, as in the arrangement indicated in Figure 2,'in which the linear oscillator 10 is connected in parallel, with respect to the high frequency energy, with another similar linear oscillator 20, the two being joined at their ends or cur- .rent nodal points, and each being provided connected in series, and are therefore heated by the sleet melting current. The center portion where no. melting takes place is at low potential, and chan es in c pacitance there have little or no e ect on t e tuning.

The arrangement shown in Figures 1 and 2 radiate energy, and to overcome this the arrangement shown in Figure 1 may be rearranged as in Figure 3, the oscillator being bent in bifilar form, so that it is substantially non-radiating. In this case also, the oscillator, in order to be an electrical half wave in length, may have to be slightly different from a half wave in physical length, but the true requirement is, of course, that it should be in tune with the wave being carried by the line. 7

The arrangement shown in Figure 3 may be provided for sleet melting, like the arrangement shown in Figure 2, by bending the double oscillator, as has been indicated in Figure 4.

The result is an arrangement which is difficult to handle, in practice, but by simply rearranging it so that the oscillators 10 and 20 are bent in bifilar form in opposite directions, it takes the convenient form shown in Figure 5.

The construction used in actual practice is illustrated in Figure 6, in which the impedance matching deviceis an insulated section of line 40, of variable effective length, which is directly tensioned between the lines 24 and the lines 68, which may be a branched line, as shown, through-tension insulators 22, 24, 26 and 28. The two wires of the insulated section 40 are connectedtogether at their ends by short pieces of conductor 42 and 44, which are overlapped and electrically separated to form the blocking condensers 30. The electrical length of the insulated circuit is preferably two half waves, but may be a greater number, to form a trap circuit which resonates the energy being carried by the lines. With a two half wave lengthtrap, portion 10, 42, 30, 42, 10, and the portion 20, 44, 30, 44, 20, are respectively equivalent to the oscillators 10 and 20 in any of Figures 2, 4 and 5. The line 24 is connected to the oscillator 10 by the jumpers 32 and 34, the points of connection of the jumpers 32 and 34 to the lines 1010 being so adjusted by movement of the connectors that the impedance of the oscillator 10 between the points of connection matches the impedance of the line 2-4. Similarly the line 6-8 is connected to the oscillator 20 by jumpers 36 and 38, the points of connection of which are so chosen by movement of the connectors 52'that the impedance therebe tween matches the impedance of the line 68. Either or both of the cross connections are made movable, as is indicated by the dotted position of the cross connection 42 at 62, in order to tune the trap circuit.

If the arrangement shown in Figure 6 is divided in half by a longitudinal axis passing through the condensers 30, 30, and the latter are grounded, the upper half may be used to match impedances when employing a single wire transmission line, as is illustrated in Figure 7. The oscillators 10 and 20 in this case are preferably quarter wave oscillators. but extra half waves of line may be inserted between the insulators 22 and 26 without deleterious effect other than to increase the length of conductor in which circulating currents flow.

I claim:

1. An arrangement for matching line impedances comprising input and output lines to be matched and a linear oscillator each of said lines being directly symmetrically coupled to the oscillator at points so spaced that the desired impedance therebetween is obtained.

2. An arrangement for matching line impedances comprising input and output lines to be matched and a linear oscillator a half wave long. each of said lines being directly symmetrically coupled to the oscillator at points so spaced that the desired impedance therebetween is obtained.

3. An arrangement for matching line impedances without interrupting the sleet melting circuit of the lines comprising the lines to be matched, a linear oscillator a half wave long, each of said lines being directly symmetrically coupled to the oscillator at polnts so spaced that the desired impedance therebetween is obtained, and a blocking condenser inserted at the potential node of the oscillator so that the oscillator does not short circuit the lines with respect to the sleet melting current.

4. A sleet melting arrangement for matching line impedances comprising the lines to be matched, a plurality of linear oscillators each a half wave long connected at their current nodal points so as to be in parallel for the high frequency current and in series i for the sleet melting current, blocking condensers inserted at the potential nodal points of the oscillators. one of said lines being directly symmetrically coupled to one of the oscillators at points so spaced that the impedance therebetween equals the impedance of the line coupled thereto and the other of said lines being directly symmetrically coupled to another of said oscillators at points so spaced that the impedance therebetween matches the impedance of the line coupled thereto.

5. A non-radiating arrangement for matching line impedances comprising the lines to be matched, a linear oscillator bent in bifilar relation and of proper length to tune to the frequency of the energy being carried by the lines, each of said lines being directly symmetrically coupled to the oscillator at points so spaced that the desired impedance therebetween is obtained.

6. A non radiating arrangement for matching line impedances provided for sleet melting comprising the lines to be matched, a plurality of linear oscillators bent in bifilar relation and connected together at their ends, each being proper in length to tune to the frequency of the energy being carried by the lines, blocking condensers inserted at the potential nodal points of the oscillators, one of said lines being directly symmetrically coupled to one of said oscillators at points so spaced that the impedance therebetween matches that of the line coupled thereto, and the other of said lines being directly sym metrically coupled to another of the oscillators at points so spaced that the impedance therebetween matches the impedance of the line coupled thereto.

7. A non radiating arrangement for matching line impedances provided for sleet melting comprising the lines to be matched, a plurality of linear oscillators bent in bifilar relation in opposite directions, and connected together at their ends, each being proper in length to tune to the frequency of the energy being carried by the lines, blocking condensers inserted at the potential nodal points of the oscillators, one of said lines being directly symmetrically coupled to one of said oscillators at points so spaced that the impedance therebetween matches that of the line coupled thereto, and the other of said lines being symmetrically coupled to another of the oscillators at points so spaced that the impedance therebetween matches the impedance of the lines coupled thereto.

8. An arrangement for matching line impedance comprising an insulated section of line tensioned between the lines to be matched thru tension insulators, means connecting the insulated section of line at its ends to resonate the energy being connected by the line, and jumpers coupling each line outside the insulator to the line inside the insulator at points so chosen that the impedances of the lines are matched.

9. An arrangement for matching line impedance comprising an insulated section of line tensioned between the lines to be matched through tension insulators, means including blocking condensers connecting the two lines of the insulated section of line together at their ends, the length of the insulated trap circuit thus formed being proper to resonate the energy being carried by the lines, and jumpers coupling each of the lines outside the insulator to the trap circuit inside the insulators at points so spaced that the impedance therebetween matches the impedance of the line connected thereto.

10. An arrangement for matching line impedances com rising an insulated section of line tensioned tween the lines to be matched through tension insulators, means including blockin condensers connecting the two lines of the insulated section of line together at their ends, the len h of the insulated trap circuit thus forme being an electrical wave in length for the energy being carried by the lines, and jumpers coupling each of the lines outside the insulator to the trap circuit inside the insulators at points so spaced that the impedance therebetween matches the impedance of the line connected thereto.

NILS E. LINDENBLAD. 

